The arrangement and distribution of alphabetic symbols or characters on alphanumeric keypads so that the keypad is easy to use and does not create excessive ambiguity in creating multiple words with the same keystrokes is difficult to achieve due to the small size of such keypads. This problem is especially pronounced in those alphabets having greater numbers of symbols than those of Roman-based alphabets, e.g. the twenty-six Roman letter alphabet. The alphabetic character layout is more easily done on keyboards for desktop systems adapted for two-handed input as the keyboard generally has thirty-six alphanumeric keys readily available for symbol placement. As is apparent, the fewer number of keys in keypads complicates layout designs, especially with those languages having large alphabets.
One goal in arriving at a keypad layout is that the symbols appear on the keys in a regular or intuitive arrangement so that users can readily become familiar with where the different symbols are located in the keypad. In this manner, the keypad is easier to use and allows the user to become more proficient in its use for fast and accurate input of the symbols. The other goal is to distribute the symbols efficiently so as to minimize the ambiguity created when a given sequence of key inputs is undertaken to form a word. Ambiguity is created when the same sequence can create multiple words. Each time the user has to go through the process of choosing a word among several, overall input speed and efficiency is slowed particularly where the number of words to be selected is high. Accordingly, it is desirable to distribute the symbols such that a minimum of such multiple word formations can be created from a given sequence of key inputs.
One problem that is noted is that the most efficient distribution of symbols on a keypad may not produce a very regular arrangement for ease of use of the keypad. On the flip side, the most regular arrangement of the symbols on the keys will generally not be the most efficient distribution of the symbols for low input ambiguity. For instance, the typical layout on a keypad for the twenty-six Roman letter alphabet is having the letter symbols appear in alphabetical order on a row-by-row basis (herein referred to as, “the ABC keypad”). As is apparent, this is a highly regular layout that allows a user to quickly become familiar with the location of the letters in the ABC keypad particularly with users having native languages that are read in a left to right fashion. On the other hand, the ambiguity of this layout is very high as commonly used letters appear on the same key and letters that are less commonly used also appear together, e.g. letters G, H, I on key four vs. letters W, X, Y on key nine. So, for example, the same sequence of key inputs that produces the word “good” will also produce six other words for a total of seven possible valid candidates from the same keystroke sequence.
Also, and as mentioned, this problem of finding the optimum balance between regularity and efficiency in the arrangement and distribution of alphabetic characters on a keypad is exacerbated where the number of symbols in the alphabet is higher than that of the Roman alphabet. One such example is Chinese alphabets, and in particular the Romanized phonetic alphabet for (Mandarin) Chinese called “Pinyin”. Pinyin evolved from “Bopomofo,” a pictorial phonetic alphabet developed early this century for Mandarin Chinese. Pinyin is the only Chinese phonetic alphabet accepted by ISO (International Standard Organization). While Pinyin uses the same twenty-six letters as the Roman alphabet, certain of its symbols are combinations or strings of the Roman letters such that Pinyin has sixty phonetic symbols which creates organizational problems in the small keypad setting, as described above. When discussing the Pinyin alphabet, it will be understood that the term symbol refers to either single or multiple Roman letter characters that stand alone in the Pinyin alphabet as single or compound character symbols, respectively.
Currently, there are no keypad layouts that are specifically designed for Pinyin-based Chinese character text input on hand-held devices, such as mobile phones or the like. Instead, what is in use today is the standard Roman letter alphabet ABC keypad layout as described earlier. Again, while this keypad layout is regular and easy to master, it is not particularly well suited for Pinyin, as it is neither regular nor efficient. The ABC keypad layout does not take advantage of specific regularities found in the Pinyin alphabet nor does it utilize keys economically. Of the twelve keys available, only eight keys (key two to key nine) are utilized for text input. Another problem with the ABC keypad layout is that among the eight text input keys, key five, seven and nine are only used for input of the first or initial letter of a Pinyin syllable, as every letter associated with those keys are consonants. As Chinese is a highly syllabic language as will be described more fully herein, concentration of consonants on a few number of keys invariably leads to ambiguities such as where different consonants combine with the same vowels to each form valid syllable candidates. For example, the key sequence 7-8-6 generates five different Pinyin syllables: “gun,” “run,” “ruo,” “sun,” and “suo”.
A further problem in efficiency relates to the number of keystrokes required to enter a Pinyin syllable. Because the ABC keypad layout is primarily designed for the Roman alphabet, it does not consider the fact that many of the Pinyin symbols are formed by combinations of Roman characters, as previously mentioned. Accordingly, to address these compound character Pinyin symbols, one has to undertake multiple key inputs. For instance, the Pinyin syllable “zhuang” composed of two Pinyin compound symbols requires six key presses to be entered. Requiring six key presses to enter a single syllable does not produce a very user-friendly keypad layout and slows down textual input speed.
Accordingly, there is a need for a keypad layout having an improved combination of regularity and efficiency for textual input. More particularly, a keypad for Chinese text input, i.e. the Pinyin phonetic alphabet, is needed having a highly regular and efficient layout.